Telescopic hydraulic mine roof support



Dec. 16, 1952 G. H. DOWTY a B J Inventor 6202 15 /7 Don 777 A ttorn e ysPatented Dec. 16, 1952 TELESCOPIC HYDRAULIC MINE R SUPPORT George H.Dowty, Cheltenham, England, assignor to Dowty Equipment Limited,Cheltenham,

England Application November 8, 1948, Serial No. 58,949 In Great BritainJanuary 12, 1948 9 Claims. (01. 121' 40) This invention relates tohydraulically actuat- I ed telescopic struts intended primarily for useas props in shoring up ceiling sections in mines.

The invention is concerned with that type of strut or prop whichcomprises a ram, usually hollow to constitute a liquid reservoir, whichacts as a plunger in an upright external cylinder which below the ramconstitutes a pressure chamber, so that extension can be effected bypumping pressure fluid from the reservoir into the pressure chamber, andcontraction can be effected by relieving or venting the pressure in suchpressure chamber back to the reservoir by way of a valvecontrolledreturn duct. Contraction may occur automatically when the roof weightexceeds a predetermined weight, and whether or not contraction isautomatic, it must occur under manual control when it is desired todislodge and remove the prop.

According to the present invention, contraction whether automatically ormanually effected occurs by opening of a single valve, which isordinarily biased to closed position but which is so connected to anexternal prop-handling member that a pull upon the latter from a safedistance will open the valve. Continuation of the same pull acts,through a first lost-motion connection, to pull aside or drag away theprop. A biasing force, which may be the one which biases the valve toclose, or a different one, serves to maintain the prop-handling memberin a given relationship to the props casing and to the first lost-motionconnection, such that that member must be pulled in a manner to open thevalve and to bottom the lost-motion connection before it is effective todrag away the prop. The connection of thevalve to the prop-handlingmember is preferably arranged, through a second lost-motion connection,which not only supplements the action of the first lost-motionconnection in allowing automatic opening of the valve for relief withoutcorresponding movement of the prop-handling member from that givenrelationship, in the event pressure within the return duct exceeds apredetermined pressure, but has the further advantage that a blow onexterior valve-operating parts can not be transmitted to the valveitself, to damage or to jam it under the rough treatment to which it isnecessarily subjected in use. By enabling the single valve to functionautomatically as a relief valve and manually as a return or unloadingvalve, by 10- eating the valve in the upper portion of the easing, formovement transversely thereof, and by locating the prop-handling memberin close relationship to the valve, and by insuring that the valve cannot be damaged or jammed by external forces, certain advantages occur inthe dislodgement of the prop by a pull from a distance upon theprop-handling member, all as will appear in detail hereinafter.Moreover, as the condition of the prop or strut'at the time withdrawalis desired is generally such that the pressure of the actuating fluidacting on the valve and tending to unseat it will substantially balancethe force acting on the valve by the control member and tending to seatit, the magnitude of the pull on the control member necessary to bringabout contraction of the prop or strut is very small indeed.

It is preferred to form the control member in two parts with the secondlost-motion connection between them whereby the relief valve and itsseating are not subject to shocks caused by inward blows directedagainst the external part of the control member. As a further protectionto the valve the external part of the control member associated with thevalve is preferably enshrouded by a rigid shield extending out from theram.

A prop or strut in accordance with the invention can very convenientlybe removed from a position of support by attaching a cord or cable tothe outer end of the control member and by pulling the cord or cablefirstly to relieve the pressure in the chamber below the ram andsecondly to cause the prop or strut to topple over about its lower end.The operator can thus 'remove the prop orstrut while standing a safedistance away from the supported area, and he can remove the fallen propor strut by dragging it endwise towards him. Its construction to theseends is a very important safety consideration in a pit prop.

In order that the invention may be more clearly understood and morereadily carried into efiect, one embodiment of pit prop in accordancewith the invention will now be described by Way of example withreference to the accompanying drawings, wherein:

Figure 1 is an axial sectional view of the upper end of the pit prop,and Figure 2 is a similar View of the lower end thereof, being in effectan axial continuation of Figure 1;

Figure 3 is a perspective view of the upper end of the prop,illustrating particularly the prophandling member, and

Figure 4 is a detail, in side elevation, and partly broken away, of thefirst lost-motion connecting means, between the prop-handling means andthe casing.

The prop shown comprises a hollow tubular ram I which is closed at itsupper end 2 and is slidable at its lower end telescopically within anouter cylinder 3 closed by a foot piece 4. The lower end of the hollowram I mounts a c1osure disc which is glanded at 6 to the inner surfaceof the cylinder 3. The closure disc 5 is rigid with a co-axial tube Iwhich extends for a short distance upwards into the ram to form thecylinder for the piston 8 of a reciprocating pump. The piston 8 has aconnecting rod 9 extending upwards through the ram to where it ispivotally connected to the pin II) of a crank II which can be oscillatedbetween stops from the outside of the ram I by a detachable handle (notshown) engaging the square-section end of the crankshaft I2. The piston8 and the closure disc 5 have appropriate non-return valves I3 and I4respectively whereby reciprocatidn of the piston 8 causes actuatingfluid to be transferred from the interior of the ram I through the valveI I into the cylinder space below the ram I.

Just below the upper end of the ram I there extends transversely acrossthe ram, rigidly connected thereto, a generally tubular housing I5 for arelief valve. The housing I5 has a transverse partition I6 situatedwithin the ram, which partition I5 is formed with a co-axial passage IIleading into a radial passage I8 which is in communication with thecylinder space below the ram I by means of a fixed tube I9 extendingdown from the partition I6 and through the closure disc 5 at th bottomend of the ram. A ball valve co-operates with the seating formed by thepassage I! and is pressed against the seating by a piston member 2|,which in eifect is part of the valve, which is glanded at 22 to theinner surface of the housing I5 and is pressed against the ball 2!] by aspring 23 which bears at one end against the piston 2| and at the otherend against an annular abutment 24 which is externally threaded andscrewed a selected amount into the outer end of the housing I5. Thepiston 2| is rigid with an apertured co-axial cup 25 having within thecup the head of a bolt 25 which extends out through the cup and isscrewed into a control member 2'! which extends through the annularabutment 24 to the outside of the ram. The control member 2'! and bolt26 are in effect integral. The thickness of the head of the bolt is lessthan the depth of the cup 25 so E that there is lost-motion connection(referred to above as the second lost-motion connection) between thecontrol member 27 and the piston 2!. A cross pin 28 extends through thecontrol member 2'! and with clearance through holes 29 in the housingI5. This clearance is part of the first lost-motion connection, referredto above. A handling loop 30 is attached to the ends of the cross pin28, and ordinarily hangs downwardly therefrom. The part of the housingI5 which is external of the ram I serves as a protection for the controlmember 2?. If, despite this precaution, the control member 21 should besubjected to any blows, the lost-motion will ensure that these will notbe imparted to the ball valve 20.

At the opposite end of the housin 25 there is provided an air valve 3|of rubber or like material. This valve 3% can be depressed from theoutside against a spring 32 to permit air to pass into the upper part ofthe ram through three equally spaced passages of which one is shown inthe drawingat 33. The valve 3! is hollow and has a breather slit 3dthrough which air may escape from within the ram. The valve 3I thusensures that the air pressure in the upper part of the ram will notdepart substantially from atmospheric pressure.

It is intended that the ram will be filled with hydraulic fluid to thelevel indicated at 35. This level will be difierent for props ofdifferent lengths. The filling operation can be achieved by unscrewingthe end plug 33 and by tilting the prop so that the hydraulic fluid canbe poured into th ram through two of the passages 33 whilst, air isescaping through the other passage 33. When the requisite amount offluid has been poured into the ram, the plug 33 with the air valvetherein is replaced.

It will be seen that the end closures 2 and Q at the upper and lowerends respectively of the prop extend in the radial sense to formflanges. These increase the areas of support, and if the prop shouldtopple over, act to safeguard the tubes I and 3.

In use it is frequently necessary to tap the lower part of the prop witha hammer in order to adjust its vertical disposition. Also the prop isliable to receive shocks and blows from other sources. It will berealized that it is desirable to avoid denting or distorting the tube .3which forms the cylinder for the glanded closure disc 5 of the innertube or ram I and it is therefore proposed to provide around the tube 3a protection in the form of a spaced outer tube 31 which is secured tothe flange of the foot piece 4 and is resiliently located at its upperend by a collar 38 of rubber or the like. If desired, however, the tube37 may be secured rigidly to the ring 39 which retains the seal 43.Again the tube 3 may be protected by an outer covering of rubber whichextends down to the flange of the end closure 4.

One convenient method of assembling the various parts of the prop is asfollows:

The housing I5 is first passed through diametrically opposite bores inthe thickened upper part 4| of the ram I. Next the pressure relief tubeI9 is entered into its radial bore in the housing I5 and welded to thehousing. The housing I5 is then correctly positioned radially of thethickened part H of the ram and welded to it at 42.

After this the upper end closure 2 is welded in position. This completesone unit subject to assembly of the relief and air valve mechanismv Nextthe piston 8 is secured to its connecting rod 9 and the rod 9 andcrankshaft are assembled in the short housing 43. This assembly ispassed through the tube I and the housing 43 is entered in the boreformed to receive it in the tube I. The housing 43 is then Welded to thetube. The first unit is now passed down, into the tube I and is securedby welding at 44. Next the bearing sleeve 45 together with the packingMI and the ring 39 are slipped along the tube I from its lower end. Theclosure disc 5 with the tube I welded thereto is entered into the lowerend of the tube I so that the tube I receives the piston 8 and the tubeI9 is received in the corresponding bore in the disc 5. The disc 5 cannow be welded to the lower end of the tube I at 46, and the tube I9welded to the disc 5. After the gland 6 and the valve I4 have beenassembled on the closure disc 5, the prop is completed by threading overthe tube I the assembly comprising the tube 3, the foot piece 4 and theprotecting tube 37. The sleeve 38 is of course positioned around theupper end of the protecting tube 3! and the ring 39 for the gland 40 iswelded to the upper end of the tube 3.

When the prop is to support a ceiling section, the pump is operated totransfer actuating fluid from the reservoir within the hollow ram intothe 'cylinderfspace below the ram. The prop will then extend and beclampedbetween the floor and ceiling. If the roof weight should exceed apredetermined weight due to the tendency for the roof to sag, the liquidacting on the relief valve 20, 2| will unseat the valve against theinfluence of the spring 23 acting through the pis: ton member on thevalve. The prop will thus accommodate itself to the increasing roofweight. When it is desired to Withdraw the prop a cord or cable ishooked on to the loop 30 and is pulled to withdraw the piston member 2|awayfrom the valve which latter is thereby freed to unseat under thepressure of the actuating fluid which can thus flow from below the ram Ithrough the tube I9 and passages I! and 4'] back into the ram I. Therelief valve is therefore used also as an unloading valve. It will beappreciated that when withdrawal is required there will be aconsiderable roof weight acting on the prop so that the forces acting inopposition on the relief valve will more or less balance, with theresult that the pull necessary to bring about unseating of the reliefvalve will be'very slight. When the prop has contracted sufficiently,continued pull on the cord or cable will cause the prop-to topple overabout its base so that the prop can then be dragged endwise towards theoperator who is standing at a safe distance away. The air valve 3| isprovided to permit air to pass into the upper end of the ram I when aconsiderable extension of the prop is being brought about by operationof the pump. There would otherwise be created in the ham a partialvacuum which would interfere with the proper operation of the pump. Alsowhen the prop contracts a considerable amount the air in the upper partof the ram is correspondingly compressed and some of it may escape byforcing its way through the breather slit 34 in the valve.

I claim:

1. In a telescoping hydraulic jack for use as a pit prop in mines, jackcasing formed of two relatively collapsible and extensible membersdefining an expansible-volume work chamber therebetween, a storagechamber in one of the members, said storage chamber containing and thework chamber being filled with a motive fluid during operation as aprop, admission duct and valve means between the chambers permittingflow of such fluid from the storage to the work chamber, a return ductbetween the chambers, means to apply pressure to the fluid to move thefluid from the storage to the Work chamber for extending said members, aprop-handling member adapted to receive a pull for dragging the prop, areciprocable, lost-motion connecting means interconnecting saidprop-handling member and said casing, holding means normally operable tohold said prop-handling member in a given relationship to said casingand yielda-ble by a pull on said prop-handling member to enable thelatter and said lost-motion connecting means to move relative to saidcasing from said given relationship into positive pulling engagementwith said casing with the lost motion of said connecting means taken up,and a valve normally closing such return duct and operatively connectedto said prop-handling member for release from such closed position andcollapse of the extensible members upon movement of the pulledprop-handling member following yielding of said holding means.

2. A hydraulic pit prop as inclaim 1, wherein the prop-handling member iformed as a handle loop, and the lost-motion connecting means comprisesa pivot pin for said handle loop, and a slot in the casing receiving andguiding said pivot pin for displacement transversely of its pivot axis.

3. A hydraulic pit prop as in claim 1, including a bolt interconnectingthe valve and the prophandling member and guided for movement from valveclosed position, wherein the prop-handling member is in the givenreltionship, to valve-open position, wherein the prop-handling memberhasmoved through the lost-motion connecting means into positive pullingengagement with the casing, and including further a spring reactingbetween the'casing and the valve to close the latter and acting throughsaid bolt to return the prop-han dling member to such givenrelationship, said spring constituting the holding means.

4. In a telescoping hydraulic jack for use as a pit prop in mines, ajack casing formed of two relatively collapsible and extensible membersdefining an expansible-volume work chamber therebetween, a storagechamber in one of the members, said storage chamber containing and thework chamber being filled with a motive fluid during operation as aprop, admission duct and valve means between the chambers permittingflow of such fluid from the storage to the work chamber, a return ductbetween the chambers, means to apply pressure to the fluid to movethefiuid from the storage to the work chamber for extending saidmembers, a valve located in and controlling communication through saidreturn duct, holding means retaining said valve normally in closedposition, whereby to maintain the prop extended in load-bearingcondition, a prop handling member adapted to receive a pull for draggingthe prop, said holding means being operatively connected to said prophandling member to retain the latter in a given relationship to saidcasing means, but being yieldable by a pull on said prophandling member,initially to enable opening of said valve and collapse of the extensiblemembers, and a 1ostmotion connectin means interconnecting saidprop-handling member and said casing means, to enable initial opening ofthe valve by a pull on the prop-handling member,;

and to bring said prop-handling member into positive pulling engagementwith the casing means when the lost motion of said connecting means hasbeen taken up by such pull.

5. A hydraulic pit prop as in claim 4, wherein the prop-handling memberis located adjacent an end of the casing means, whereby continued pullthereon after opening of the valve and subsequent positive pullingengagement of said prop handling member, will enable the prop to bedragged away endwise by a pull initiated from a distant point.

6. A hydraulic pit prop as in claim 4, including a bolt interconnectingthe valve and the prophandling member for positive movement of saidmember to its given relationshi upon movement of the valve to closedposition, a spring urging the valve into closed position andconstituting the holding means, a second lost-motion meansinterconnecting the bolt and one or the other of the prop-handlingmember and the valve, for opening of the valve in opposition to saidspring for relief of duct pressure in excess of a predetermined value,independently of movement of said prop-handling member.

7. A hydraulic pit prop as in claim 4, including an elongated valvehousing directed transversely of and secured rigidly to the casingadjacent its upper end, the return duct including said valve housing,and the valve being guided in and for opening and closing movementlengthwise of said housing, means including a bolt interconnecting theprop-handling member and the valve, through the housing, a springconstituting the holding means and reacting between the valve housingand the valve to hold the latter yieldably closed, and through said bolturging the prop-handling member into its given relationship to thecasing, said prop-handling member being arranged for operative movementfrom such given relationship by a pull in a direction generallytransverse to the casing.

8. A hydraulic pit prop as in claim 7, wherein the bolt is fixedlyconnected to the prop-handling member, and including a secondlost-motion means forming part of the interconnection between theprop-handling member and the valve, said second lost-motion meansincluding a head on the bolt, and a shouldered guide on the valveengageable with the bolts head to urge thelatter and the prop-handlingmember into the latters given relationship upon closure of the valve,but permitting opening of the valve for relief, independently ofmovement of the prop-handling member from such given relationship.

9. A hydraulic pit prop as in claim 4, including an elongated valvehousing directed transversely of and secured rigidly to the casingadjacent its upper end, the return duct including said valve housing,and the valve being guided in and for opening and closing movementlengthwise of said housing, means including a bolt interconnecting theprop-handling member and the valve and directing lengthwise of the valvehousing, a spring constituting the holding means, disposed within thecasing and urging the valve into closed position, and through said bolturging the prop-handling member into its given relationship to thecasing, and the prop-handling member being formed as a handle looppivotally hung from said bolt, externally of the casing, for pullingengagement from a distant point to release the valve and to drag awaythe prop.

G. H. DOWTY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 151,670 Ojeda, June 2, 18741,133,270 Dale Mar. 30, 1915 1,598,426 Ditson Aug. 31, 1926 1,706,309Miller Mar. 19, 1929 1,805,588 Manley May 19, 1931 2,284,2 8 Page May26, 1942

